Low temperature fluorination of Sr2-xBaxCuO3 (x = 0.0-0.6) was carried out. The pristine samples were heat-treated with NH4F at 210 °C in flowing nitrogen gas. The major phase was drastically changed to the K2NiF4 type, one with poor crystallinity. The fluorinated samples exhibited Meissner signals, but the signal intensity was too low to identify the corresponding superconducting phase correctly. A maximum Tc of 68 K was detected in the fluorinated sample with x = 0.2, being different from Slater et al.'s previous result in which the fluorinated sample with x = 0.6 exhibited the maximum Tc of 64 K. The crystallite size of the K2NiF4 phase in the fluorinated sample with x = 0.2 was estimated to be about 220 angstroms from a broad peak of the 220 reflection in the X-ray powder diffraction (XRD) pattern. It is considered that the major phase with the K2NiF4 structure is responsible for the observed superconductivity and the small Meissner signals were attributed to the small grain size. In 6 months, the orthorhombicity of the K2NiF4 phase in the fluorinated sample with x = 0.2 increased and the observed Tc was appreciably lowered. This correspondence between the orthorhombicity and Tc also implies that the detected Meissner signals came from the K2NiF4 phase.
ASJC Scopus subject areas
- Electronic, Optical and Magnetic Materials
- Condensed Matter Physics
- Energy Engineering and Power Technology
- Electrical and Electronic Engineering